Electrostatic means for liquid dispersion in minute droplets are used in a variety of technological applications, such as paint spraying, ionization for chemical analysis, drug inhalation, synthesis of particles from liquid precursors, and surface coating, by way of example and not limitation. The class of atomizers in which the dispersion of the liquid is driven exclusively by electric forces is referred to heretofore as electrospray (ES). Within this class of atomizers it is often desirable to tightly control the size distribution of the resulting aerosol. Such a system can be implemented by feeding a liquid with sufficient electric conductivity through a small opening, such as the tip of a capillary tube or a suitably treated “hole”, maintained at several kilovolts relative to a ground electrode positioned a few centimeters away. The liquid meniscus at the outlet of the capillary takes a conical shape under the action of the electric field, with a thin jet emerging from the cone tip. This jet breaks up farther downstream into a spray of fine, charged droplets. In view of the morphology of the liquid meniscus, this regime is labeled as the cone-jet mode.
Among the key features that distinguish the cone-jet electrospray from other atomization techniques are: quasi-monodispersity of the droplets; Coulombic repulsion of the charged droplets, which induces spray self-dispersion, prevents droplet coalescence and enhances mixing with the oxidizer; and the use of a spray “nozzle” with a relatively large bore with respect to the size of the generated droplets, which implies that liquid line obstruction risks are minimized. The cone-jet mode can produce droplets/particles over a wide size range, from submicron to hundreds of micrometers, depending on liquid flow rate, applied voltage and liquid electric conductivity. Especially in the submicron range, the capability of producing monodisperse particles with relative ease is relatively unique as compared to other aerosol generation schemes.
Electrospray Ionization Mass Spectrometry (ESI-MS), spearheaded by the work of John B. Fenn at Yale in the 1980's, is a practical application of the electrospray in widespread use. Key drawbacks that have hampered applications to other areas are: the low flow rates at which the cone-jet mode can be established and the restrictions on the liquid physical properties of the liquids that can be dispersed with this technique. The difficulty is particularly severe in applications requiring that the initial droplet size be small, as for example in drug inhalation or nanoparticle synthesis.
The present invention was originally conceived for small-scale combustion of liquid fuels, which has become increasingly important, especially for small portable energy systems that are designed to be carried by an individual. For example, it may be desirable to equip a soldier with a lightweight and compact sources of electrical power and microclimate control, instead of more cumbersome and bulky battery packs. An electric power source based at least in part on the combustion of liquid fuels would exploit the much larger power density of liquid hydrocarbon fuels as compared to the best batteries currently in use today.